1. Field of the Invention
The present invention relates to an exchange system, and in particular, a method for controlling and processing an incoming call of a line-busy keyphone system.
2. Description of the Related Art
Generally, private exchange systems, such as keyphone systems, have an off-hook ring service function for ringing a busy tone to a keyphone, in the case that a calling part of an extension station wants to call a calling part of the keyphone during call between another calling part of the extension station and the calling part of the keyphone. The aforesaid function therefor is conventionally to ring an off-hook ring to only a line-busy keyphone. As a result, even though the user, who is calling, can know the fact that the call is made, he can not know the counterpart's telephone number to be called. For example, when a director calls out his secretary or an emergency call is made from the director in the place such as a company, the user should hold on or ring off a current call in order to speak to him over a ringing call. Accordingly, there has been a problem in which because he can not check which call is important between the current call and the ringing call, he can not provide a proper service due to answering the ringing call late.
U.S. Pat. No. 4,991,203 to Katsuhiro Kakizawa entitled Line Switching Apparatus And Method describes a known method of placing a calling extension in a camp-on-busy state when a called extension is determined to be busy.